UPDATE (Aug. 8, 9 a.m. PT) — Nearly two dozen government officials met Wednesday to discuss different retrofitting options for one of the state’s most important and imperiled water sources.
Scoggins Dam was built in the early 1970s to hold back water from the Tualatin River to form Hagg Lake. In recent years, it has been classified as a seismically at-risk dam that needs to be modified in order to reduce downstream hazards in the event of a large earthquake.
Hagg Lake is the primary water source of Washington County’s estimated 600,000 residents. Officials are looking for new ways to increase water storage for the county’s growing population.
Washington County’s Clean Water Services and the U.S. Bureau of Reclamation are working together to address the at-risk dam. They created the Tualatin Basin Joint Project, which is exploring three options for the dam — two at the location of the current dam and one downstream.
“So now we’re to the point where we gathered all the engineering information and so now we are starting to gather the environment information and working together under the Tualatin joint project to basically design, build whatever the alternative that’s chosen,” Clean Water Services water supply manager Tom VanderPlaat said.
A magnitude 9.0 earthquake off the Northwest coast could hit at any time. How can we prepare for this impending and unpredictable disaster?
The first option would modify the existing dam without raising its height. This option would make safety improvements for the dam to be able to withstand a major earthquake, but it would not provide increased water storage.
The second option would modify and raise the dam, and would allow for additional water storage. The modifications would add 17.5 feet of water depth to Hagg Lake.
The third option proposes the construction of an additional dam downstream of the Stimson Mill just east of Scoggins Dam, where the valley is narrower.
The U.S. Bureau of Reclamation will fund the dam and safety aspects of the project. Fifteen percent of the seismic improvement costs will be repaid by the local governments that share the water in Hagg Lake.
“We know that smart investments and infrastructure are very good investments in our community,” said Rep. Suzanne Bonamici, D-Ore., whose district includes Washington County. “We know this project is going to be vital for water supply but also for protecting the lives and resources in our community.”
In the region, nearly 400,000 residents, 250,000 jobs and 17,000 acres of agriculture rely on the water stored in Hagg Lake. It is currently the only water source for the city of Hillsboro.
“This project is absolutely a regional project,” Hillsboro Mayor Steve Callaway said, adding that a sufficient water supply in Washington County is also important for the entire state, given the important contribution it makes to Oregon’s tech and agricultural economies.
A decision on the three options is expected by next February.
Correction: Aug. 8, 2019. An earlier version of this story incorrectly estimated the amount of additional water storage capacity that could be achieved under certain dam retrofitting options being considered for Henry Hagg Lake in Washington County.